1. Field of the Invention
This invention relates to a process for the production of tetrahydrofuran, gamma butyrolactone, 1,4-butane diol and the like from a hydrogenatable precursor such as maleic acid, succinic acid, corresponding esters and their mixtures and the like in the presence of hydrogen and a noble metal catalyst, and more specifically to a process for regenerating spent catalyst from the process.
2. Description of the Related Art
Various methods and reaction systems have been proposed in the past for manufacturing tetrahydrofuran (THF) and 1,4 butane diol (BDO) by catalytic hydrogenation of gamma butyrolactone, maleic acid, maleic anhydride, succinic acid or related hydrogenatable precursors. Also, a variety of hydrogenation catalysts have been historically proposed for this purpose including various transition metals and their combinations deposited on various inert supports, all as generally known in the art. Many of these catalysts are proposed for use in hydrogenations carried out in an organic solvent or organic reaction media and not in an aqueous solution phase. In fact, at least one prior publication suggests that water and succinic acid may be considered as inhibitors to the desired catalysis, see Bulletin of Japan Petroleum Institute, Volume 12, pages 89 to 96 (1970).
U.S. Pat. No. 5,698,749 discloses a process for producing 1,4-butanediol by aqueous hydrogenation of a hydrogenatable precursor using a catalyst comprised of a noble metal of Group VIII and at least one of rhenium, tungsten and molybdenum, on a carbon support pretreated with an oxidizing agent. The purpose of this pretreatment is to increase the yield of butanediol relative to gamma butyrolactone or tetrahydrofuran, as compared to the use of a catalyst made with un-pretreated carbon.
On extended use of noble metal catalysts, the reaction rate for the hydrogenation typically slows down to the point where the deactivated or spent catalyst must be replaced with fresh catalyst. The old catalyst may then be destroyed by burning off the carbon, followed by partial recovery of the expensive metal ingredients. The overall cost of catalyst replacement is quite high. Similar deactivation problems are typically found with other noble metal catalysts in this process. Typically, many factors may combine to cause such deactivation, and even finding these causes may not directly lead to a method for regenerating a deactivated catalyst. While the literature describes a number of methods for regeneration of noble metal hydrogenation catalysts, many of these have failed or been found inadequate in practice.
In processes for the production of tetrahydrofuran, gamma butyrolactone, 1,4-butane diol and the like from a hydrogenatable precursor in an aqueous solution in the presence of hydrogen and a noble metal catalyst, there is a need for a more economical method for the regeneration of the spent noble metal catalysts, or for extending the active life of such catalysts.
This invention relates to a process for production of tetrahydrofuran, gamma butyrolactone, 1,4 butanediol and the like from a hydrogenatable precursor such as maleic acid, succinic acid, corresponding esters and their mixtures and the like in the presence of hydrogen using a noble metal catalyst, the improvement comprising the treatment of deactivated noble metal catalyst by contacting with from about 0.1% to about 20% of oxidizing agent relative to the dry weight of the catalyst and at a temperature ranging from ambient to about 300xc2x0 C.